My invention relates to a device for translating rotary motion into linear motion, and more specifically to such a device employing a lead screw, together with means for fine adjustment of the preload under which an engagement member is slidably engaged in the helical groove in the lead screw. The rotary to linear converter in accordance with my invention has particular utility in conjunction with an apparatus for the transfer of information with flexible magnetic disks, now commonly referred to as floppy disks, wherein a magnetic transducer head is linearly moved back and forth in a radial direction of the floppy disk for track to track accessing in response to the bidirectional, incremental rotation of an electric stepping motor.
In floppy disk drives (FDDs) the bidirectional, incremental rotation of the stepping motor must be translated into the linear stepwise travel of the transducer head to enable the latter to access the individual tracks on the disk. As an example of known rotary to linear converter of the lead screw type used in FDDs, I cite U.S. Pat. No. 3,678,481 issued to Dalziel et al. As disclosed in this patent, the lead screw is driven by a bidirectional stepping motor. The bidirectional rotation of the lead screw is converted into the linear travel of the head carriage as a rigid stylus attached to the latter is spring loaded into sliding engagement in the thread or groove of the lead screw. The spring loading of the stylus, or of any quivalent engagement means such as a ball, is normally accomplished by a leaf spring cantilevered to the head carriage.
One of the problems with this type of rotary to linear converter is the adjustment of the spring preload under which the engagement means is held against the lead screw. Generally, the greater the spring force is, up to a limit, the more faithfully will the rotation of the lead screw translated into the linear travel of the head carriage. However, any unnecessarily great spring force will impose a correspondingly heavy load on the drive motor. A precise adjusetment of the spring force on the engagement means is therefore essential for the proper operation of the converter mechanism.
An obvious solution to this problem might be the use of an adjusting screw abutting against the back of the cantilever spring carrying the engagement means on its front side. By turning the adjusting screw in either direction, the spring together with the engagement means thereon would be variably moved toward and away from the lead screw. I object to this solution. The slightest turn of the adjusting screw would result in a substantial change in the spring force on the engagement means. No fine adjustment of the spring preload would be possible in this manner.